This invention relates to the analysis of atmospheric samples for particulate contaminants. More particularly it relates to an analyzer that determines both the size distribution and chemical make-up of atmospheric aerosol particles as a function of particle size.
Fine atmospheric aerosols have recently been indicted as a serious health threat. These particles can be generated in aircraft and automobile engines, coal and gas fired power plants, painting/depainting facilities, gas discharge boiler operations and in the atmosphere through chemical reactions of gaseous precursors. In addition to being a direct health threat, atmospheric aerosols also influence the climate by scattering and/or absorbing sunlight and by altering cloud coverage, which impacts both absorption and scattering of solar radiation. Full particulate emission/ambient concentration characterization requires determining both particle size distributions and chemical content, which often varies with particle size. At present this is a time-consuming and expensive task because available commercial instrumentation can size airborne aerosol particle distributions; however, measurement of the chemical contents of aerosol particles is performed in a separate stage, using laboratory procedures. No commercial instrument is available to automatically size the particles and simultaneously determine the composition as a function of their size in real time.
The need for sophisticated instrumentation for on-line, real-time aerosol composition analysis is widely acknowledged and various groups have been engaged in developing new technology for this purpose. The prior approaches of which we are aware involved the coupling of high-power lasers to induce aerosol ablation/vaporization and ionization, followed by time of flight (TOF) or quadrupole mass spectrometric analysis. Typically a light-scattering signal caused by a particle passing through a visible laser light beam is used to detect the spatial presence of a particle and to initiate a timing sequence for the firing of the vaporization laser. Reliable and efficient coupling of the complex laser triggering circuits with high-power pulsed laser and high-vacuum mass spectrometry technology, however, is a formidable task, especially under difficult field measurement conditions.